The invention relates to a coupling assembly with two coaxial parts which are rotatable relative to one another, with one of the parts being provided with an annular chamber which contains a highly viscous fluid in which, upon relative rotation of the parts relative to one another, fluid shear is effected by means of a conveying member connected to the other one of the parts, as a result of which a pressure build-up is generated in the annular chamber for the purpose of increasing a transmission of torque between the parts, with the annular chamber being hydraulically connected to a compensating chamber with a variable volume for the highly viscous fluid, which compensating chamber is formed by an axially open annular groove and an axially movable annular element sealing the annular groove.
Coupling assemblies of this type are known from DE 43 43 307 A1 and U.S. Pat. No. 4,905,808 (FIG. 23) wherein the annular chamber is delimited by an axially movable piston loading a friction coupling assembly whose plates are alternately connected to one each of the parts rotatable to one another. In order to ensure that, when moving the piston, the annular chamber remains completely filled and for compensating for any thermal changes in volume in the friction coupling assembly, there is provided a reservoir which is formed of an axially open annular groove and an annular piston which is movable therein and loaded by plate springs.
Coupling assemblies in the sense of the invention are primarily all assemblies wherein a conveying member connected to one of the rotatable parts rotates in an annular chamber, with the annular chamber being sealed by an axially movable piston, so that a displacement of the piston requires a change in volume.
Coupling assemblies of this type, in the sense of the invention, are also conventional viscous couplings wherein the annular chamber contains a larger number of plates which are alternately connected to the two parts rotatable relative to one another. In such assemblies, a change in temperature in the enclosed viscous fluid is connected with a change in volume which may necessitate volume compensating measures.
It is the object of the present invention to provide a simple, easily sealable design for said reservoir.